1. Field of the Invention
The present invention relates to methods for producing crystals of a purine nucleoside compound which have excellent storage stability, and particularly it relates to methods for producing crystals of 2′,3′-dideoxyinosine (DDI) which are useful as a medical drug such as an anti-AIDS drug.
2. Discussion of the Background
A 2′,3′-dideoxypurine nucleoside compound has an antiviral action which is usable for an anti-AIDS drug, for example. Therefore, it can be used as a medical drug (see, for example, JP-A 61-280500 and J. Med. Chem., vol. 30, p. 440 (1987)). Various methods for producing a 2′,3′-dideoxypurine nucleoside compound have been reported until now (see, for example, JP-A 01-224390, JP-A 02-117689, JP-A 02-291291, JP-A 03-227997, JP-A 06-041129, and JP-A 06-041130).
However, crystals of 2′,3′-dideoxyinosine are decomposed during storage to produce hypoxanthine, and therefore it has been found that there is a problem in the long-term storage stability thereof.